1. Field of the Invention
The invention relates to an optical device comprising a first coupler, a second coupler and a plurality of at least three optical channels connecting outputs of the first coupler to inputs of the second coupler and forming a dispersive array.
Such a device is particularly useful as an array multiplexer or demultiplexer because of its wavelength dependent behaviour due to the dispersive array. The dispersion gives the device a wavelength selectivity in the range from 0.1 nm to about 200 nm. A wavelength division multiplexer/demultiplexer (WDM) can be used as a multiplexer in the field of optical communications to combine optical beams at pump and signal wavelengths in an optical amplifying system. WDMs can also be used to increase the transmission capacity of optical fibres by adding closely spaced wavelength bands. Different wavelength bands can be used to provide bidirectional transmission on a single fibre. A WDM also can be used as a demultiplexer to perform the operation opposite to that of a multiplexer, i.e. decomposing an incoming signal into its constituting wavelength bands.
2. Description of the Related Art
An optical device of the type described in the opening paragraph is described in the European patent application nr. 0 565 308. The known device comprises a pair of optical couplers and an array of channels extending between the couplers. The couplers are so-called radiative couplers. Such a coupler is typically a slab waveguide configured for providing substantially identical optical paths between an input channel and a plurality of coupler output channels. A drawback of the known device is the non-uniform channel response, i.e. the power transmission from an input channel to an output channel of the device depends on the ordinal numbers of the input and output channel.